1. Field of Invention
This invention relates to a process for the enzymatic synthesis of electrically conductive substituted or unsubstituted polyanilines, and to compositions comprising such polyanilines and other non-electrically conductive polymers. Another aspect of this invention relates to a method of using such polyanilines and compositions to form conducting polymer articles, including films, and to such articles.
2. Prior Art
In the field of conducting polymers there is a need to develop efficient methods of manufacture. The preferred chemical method of producing polyaniline involves reacting aniline with stoichiometric amounts of ammonium persulfate in the presence of p-toluene sulfonic acid (TSA). The reaction produces ammonium sulfate as a by-product. The TSA anion is the dopant rendering the polymer conductive. The sulfate anion by-product competes with TSA for the polyaniline protonated sites. Excess TSA is usually used in order to minimize sulfate doping of the polymer. This excess TSA has to be removed after the reaction is complete. Thus, the chemical synthesis of polyaniline produces a rather large quantity of undesirable ammonium sulfate by-product and requires excess TSA.
Others have attempted to produce polyaniline enzymatically; however, their procedures have yielded a mixture of low molecular weight oligomers and azo-linked species. Aizawa et al, in "Enzymatic Synthesis of Polyaniline Film Using a Copper-Containing Oxidoreductase: Bilirubin Oxidase", Journal of Biotechnology, 14, 301 (1990), discuss enzymatic polymerization of aniline wherein the resulting aniline polymer contains symmetric head-to-head (N-N) coupling bonds. Mann and Sanders, in "Studies in Peroxidase Action 1-The Oxidation. of Aniline" Proceedings of the Royal Society, 119 pp 47-60 (1935) also oxidized aniline enzymatically using a solution of aniline in dilute acetic acid at a pH of 4.5 with a peroxidase system. They describe their product as a mixture of related substances: 2,5-dianilino-para-benzoquinone imide-anil, indulene, pseudo-mauveine and ungreenable aniline black. On page 49 of this reference, it is depicted that ungreenable aniline black was formed by the further oxidation of quinone-anil-(4(4-aminoanilino)anil) through emeraldine and nigraniline forms of polyaniline having only eight aniline repeat units. All of these products are soluble in a large variety of solvents, which suggests that they are of low molecular weight.
The invention described herein resolves many of the disadvantages associated with chemical and enzymatic synthesis of polyaniline.